The major emphasis of the proposed research is the investigation of several types of tumor viruses as model systems to study the molecular mechanism of transformation. The areas of investigation are as follows: I. Herpes Viruses: 1. Studies to identify the genes of herpes simplex virus which are required for transformation. 2) Studies of the genome of the Epstein-Barr virus. II. Papova Viruses: Isolation and characterization of promoter mutants of SV40 to study regulation of early gene expression. III. RNA Tumor Viruses: 1. Studies of endogenous viral genomes of uninfected chicken cells. 2. Studies of the transforming gene of feline sarcoma virus.